Although the analysis of gene regulation in prokaryotes has generally focused on understanding transcriptional control, the steady-state level of any given messenger RNA is a function of both synthesis and decay. Factors contributing to transcript stability thus must be important for gene regulation, particularly in Escherichia coli, since mRNA half-lives can vary more than 50 fold, from seconds to 30 minutes. While there has been considerable speculation regarding the mechanism of mRNA decay, until recently it has been difficult to study it. The goals of this project are to understand the molecular events involved in the turnover of mRNA in Escherichia coli and to examine its regulation. To do so, we will carry out a series of biochemical and genetic experiments to study proteins involved in mRNA decay and to characterize the products of new genes that are required for mRNA turnover and cell viability. We will focus on understanding the in vivo relationships and regulation of the mrsA (messenger RNA stability), mrsC, mrsF, and rne (RNase E) genes. Additionally, we will further characterize the catalytic activities of RNase E and try to identify the biochemical functions of the MrsA, MrsC and MrsF proteins. The MrsC protein is of particular interest because it is a homolog of a unique family of eukaryotic ATP-binding proteins. A more complete understanding of mRNA turnover in prokaryotes will provide an important model for studying eukaryotic message decay.